A typical example of a driver assistance system is a so-called ACC system (adaptive cruise control). This is understood to be an adaptive cruise control system capable of regulating the speed of the vehicle at a desired speed selected by the driver and additionally having a locating system, e.g., a radar system, for locating preceding vehicles and thus, if necessary, capable of adapting the speed of the host vehicle to that of the preceding vehicle, the so-called target object. Such systems have previously been designed mainly for use on highways, but advanced ACC systems are being developed that are also suitable for use on rural roads and even in city traffic.
The target object for adaptive cruise control is usually a directly preceding vehicle in the same lane of the host vehicle. This system must therefore be capable of recognizing which lane a preceding vehicle is occupying. Therefore, a radar sensor having angle resolution is used, permitting measurement of not only the distance and relative speed of the preceding vehicle but also its azimuth angle and thus the transverse position with respect to the host vehicle.
To be able to perform a correct lane assignment, the anticipated course of the road and thus the anticipated path of the host vehicle is assessed. Frequently, the yaw rate of the host vehicle is measured for this path prediction, e.g., with the help of a yaw rate sensor, so that a curved course of the road may be recognized at least when the host vehicle has already entered the curve. In addition, the angular velocity of a group of preceding vehicles may also be used for the path prediction. If the host vehicle also has a navigation system, it is also possible to use the digital map of the navigation system to estimate the course of the road.
Path prediction then forms the basis for determining a so-called travel route envelope, which is understood to refer to a strip on the road that is somewhat wider than the host vehicle and follows the anticipated path of the vehicle. Only vehicles within this travel route envelope may then be considered as the target object for the adaptive cruise control.
There have already been proposals for varying the width or right and left boundaries of the travel route envelope depending on the situation. For example, when the host vehicle is in the outermost left lane of a multilane road, it is expedient to widen the travel route envelope to the left, so that the target object is not so easily lost in a curve to the left, whereas on the other hand, a narrower travel route envelope boundary is selected on the right side, thereby preventing so-called side lane interference due to vehicles in the right side lane. The situation is reversed accordingly when driving in the outermost right lane. To decide which lane of a multilane road the host vehicle is occupying, either the locating data of a group of preceding vehicles or the locating signals of stationary objects may be used.
On rural roads, the travel route envelope will be widened toward both sides, so that tracking of the target object is ensured even in tight curves. To recognize the type of road, whether highway or rural road, the digital map of the navigation system may be analyzed, if necessary.
In the normal case, an adaptation of the travel route envelope that conforms to the situation may be achieved in this way. However, the movement data on the preceding vehicles also enter into the determination of the travel route envelope and, if necessary, enter into the path prediction, so vehicles turning at highway exit ramps, intersections, or junctions may result in a misinterpretation of the situation and therefore a malfunction of the driver assistance system. This applies not only to ACC systems but also to safety systems (PSS, predictive safety system), for example, which warn the driver of the risk of collision or actively intervene in the guidance of the vehicle, if necessary, to prevent a collision or at least to minimize the consequences thereof.